Conventionally, an analog/digital conversion process has been realized by performing a discretization, a quantization, and an encoding, and the discretization, the quantization, and the encoding have been performed by an electrical processing using a semiconductor.
In order to speed up an analog/digital conversion by a light, a method of demultiplexing a time-multiplexed optical signal can be used in the discretization process, such as a four lightwave mixing, a nonlinear loop mirror, and a method using a harmonic generation of an optical crystal. As a method for the quantization process, a method using a higher-order solution, a method using a Raman and a self-frequency shift due to a self-phase modulation, and the like are used.
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-10129
Nonpatent Document 1: Takashi Yamamoto, et al., “Demultiplexing of sub-terabit TDM optical signal using an ultra-high speed nonlinear optical loop mirror”, IEICE Transactions, C-I, The Institute of Electronics, Information and Communication Engineers (IEICE), Vol. J82-C-I, Pp. 109-116, March 1999